<!--
外边距
    控制盒子和盒子之间的距离
    可以给四个方向加上边距
        margin-top
        margin-bottom
        margin-left
        margin-right  
        
    块级元素水平居中
    margin:auto

    去除浏览器默认样式
    * {
        margin:0;
        padding:0;
    }
-->

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        div {
            border: 5px solid green;

            width: 200px;
            height: 200px;

            /* margin-top:5px;
            margin-bottom:5px;
            margin-left:5px;
            margin-right:5px; */
            margin: auto;
        }
    </style>

</head>

<body>
    <div></div>
    <div></div>
    <div></div>
</body>

</html>




